Generally, it does not matter if you use AMD or Intel since audio recording is not that intensive compared to video, with the exception that you run gigabytes of samples. In that case, you need an Intel since tests have shown that Intel cpus have the performance advantage when it comes to running loads of sample libraries. I should know... been designing and building powerhouse DAWs for Gerard Salonga since 2008.
As for the i5, you have to pair it up with good ram and a good motherboard. Some people prefer Asus, but I've had some probs with recent Asus boards over the years... same with MSI. Best for now are Gigabyte boards. For ram, get branded ram with good specs and go at least 4 gigs - win7 64-bit somewhat struggles at 2 gigs. Make sure to power these up with a good PSU as well - no generic power supplies please!
As for obsolescence, any design now will last maybe 2 or 3 years at the most. Just build your DAW for now, stock it up with a mature OS like win7 (not win8 yet!). If you decide 64-bit, make sure most of your software can support it. If not, stick to 32-bit for the most part,or even go XP as I find this to support a majority of hardware plus some very good audio interfaces from a few years back.